Anticonvulsant and antiretroviral interactions

Virus-Induced Epilepsy vs. Epilepsy Patients Acquiring Viral Infection: Unravelling the Complex Relationship for Precision Treatment

The intricate relationship between viruses and epilepsy involves a bidirectional interaction. Certain viruses can induce epilepsy by infecting the brain, leading to inflammation, damage, or abnormal electrical activity. Conversely, epilepsy patients may be more susceptible to viral infections due to factors, such as compromised immune systems, anticonvulsant drugs, or surgical interventions. Neuroinflammation, a common factor in both scenarios, exhibits onset, duration, intensity, and consequence variations. It can modulate epileptogenesis, increase seizure susceptibility, and impact anticonvulsant drug pharmacokinetics, immune system function, and brain physiology. Viral infections significantly impact the clinical management of epilepsy patients, necessitating a multidisciplinary approach encompassing diagnosis, prevention, and treatment of both conditions. We delved into the dual dynamics of viruses inducing epilepsy and epilepsy patients acquiring viruses, examining the unique features of each case. For virus-induced epilepsy, we specify virus types, elucidate mechanisms of epilepsy induction, emphasize neuroinflammation's impact, and analyze its effects on anticonvulsant drug pharmacokinetics. Conversely, in epilepsy patients acquiring viruses, we detail the acquired virus, its interaction with existing epilepsy, neuroinflammation effects, and changes in anticonvulsant drug pharmacokinetics. Understanding this interplay advances precision therapies for epilepsy during viral infections, providing mechanistic insights, identifying biomarkers and therapeutic targets, and supporting optimized dosing regimens. However, further studies are crucial to validate tools, discover new biomarkers and therapeutic targets, and evaluate targeted therapy safety and efficacy in diverse epilepsy and viral infection scenarios.

Tubular Secretory Solute Clearance and HIV Infection

BACKGROUND

Tubular secretion is an important kidney function responsible for the clearance of numerous medications, including antibiotics and antivirals. It is unknown whether persons living with HIV have lower secretion compared with HIV-uninfected persons, which might predispose them to the risk of progressive kidney disease or adverse drug events.

SETTING AND METHODS

We evaluated a panel of 6 endogenous secretory solutes in 199 women living with HIV (WLWH) and 100 women without HIV enrolled in the Women's Interagency HIV Study. Secretory clearance was estimated as the urine-to-plasma ratio of each solute, with adjustment for urine tonicity. Using multivariable linear regression analysis, we compared differences in levels of secretory solute clearance between women with and without HIV and evaluated characteristics associated with secretion.

RESULTS

WLWH were older (median 40 vs. 38 years) but had similar estimated glomerular filtration rate (eGFR, 96 vs. 100 mL/minute/1.73 m 2 ) compared with those without HIV. African American and Latino race, diabetes, diastolic blood pressure, smoking, hepatitis C, peak HIV viral load, and current and nadir CD4 count were associated with differences in clearance of at least 1 marker after multivariable adjustment. The secretory clearance of 3 solutes (cinnamoylglycine, kynurenic acid, and pyridoxic acid) were on average 10%-15% lower among WLWH compared with those without HIV independent of eGFR, albuminuria and chronic kidney disease risk factors, including HCV, and injection drug use.

CONCLUSIONS

HIV is associated with reduced secretion among women with preserved eGFR. The implications of these findings for drug dosing and adverse events need to be evaluated.

Clinically Relevant Interactions Between Ritonavir-Boosted Nirmatrelvir and Concomitant Antiseizure Medications: Implications for the Management of COVID-19 in Patients with Epilepsy

Ritonavir-boosted nirmatrelvir (RBN) has been authorized recently in several countries as an orally active anti-SARS-CoV-2 treatment for patients at high risk of progressing to severe COVID-19 disease. Nirmatrelvir is the active component against the SARS-CoV-2 virus, whereas ritonavir, a potent CYP3A inhibitor, is intended to boost the activity of nirmatrelvir by increasing its concentration in plasma to ensure persistence of antiviral concentrations during the 12-hour dosing interval. RBN is involved in many clinically important drug–drug interactions both as perpetrator and as victim, which can complicate its use in patients treated with antiseizure medications (ASMs). Interactions between RBN and ASMs are bidirectional. As perpetrator, RBN may increase the plasma concentration of a number of ASMs that are CYP3A4 substrates, possibly leading to toxicity. As victims, both nirmatrelvir and ritonavir are subject to metabolic induction by concomitant treatment with potent enzyme-inducing ASMs (carbamazepine, phenytoin, phenobarbital and primidone). According to US and European prescribing information, treatment with these ASMs is a contraindication to the use of RBN. Although remdesivir is a valuable alternative to RBN, it may not be readily accessible in some settings due to cost and/or need for intravenous administration. If remdesivir is not an appropriate option, either bebtelovimab or molnupiravir may be considered. However, evidence about the clinical efficacy of bebtelovimab is still limited, and molnupiravir, the only orally active alternative, is deemed to have appreciably lower efficacy than RBN and remdesivir.

Headache in transgender and gender-diverse patients: A narrative review

OBJECTIVE

To summarize the unique aspects of managing headache in gender minorities and current research in this area including the potential relationship between gender-affirming hormone therapy (GAHT) and headache.

BACKGROUND

The study of headache in gender minorities is intrinsically important. Gender minorities are medically underserved, and their medical care to date has been limited by socioeconomic disadvantages including stigma and an unsupportive clinical environment. Despite the rising population of transgender and gender-diverse adults and youth, headache research has also been limited. Knowledge of hormonal effects on headache in cisgender patients raises the question of possible effects of GAHT on transgender patients.

METHODS/RESULTS

The manuscript is a narrative review of current best practices in treating transgender patients, including the use of appropriate terminology and ways to create a supportive environment. It also contains current guidelines on GAHT and reviews drug-drug interactions and secondary headache related to hormone therapy. We also review transgender headache research and related research on hormonal effects on headache in cisgender individuals.

CONCLUSION

Creating a supportive environment for transgender and gender-diverse patients and being knowledgeable about GAHT are key to providing quality headache care. This review identifies further research needs for this population including the epidemiology of headache disorders in sexual minorities and the potential effects of GAHT on headache disorders in transgender patients.

Assessment of Antiepileptic Drug Concentrations in HIV-Infected versus HIV-Negative Patients: A Retrospective Analysis

INTRODUCTION

A higher rate of subtherapeutic psychotropic drug concentrations was recently found in HIV-infected versus HIV-negative patients. In this study, we sought to investigate if this trend could also apply to antiepileptic drugs.

METHODS

Overall, 700 HIV-infected patients were screened during the first 2 years after the introduction of our outpatient polytherapy management service (Gestione Ambulatoriale Politerapie [GAP]) in the search for subjects with antiepileptic drug trough concentration assessments. The distribution of such concentrations was compared with that in HIV-negative patients monitored over the same period.

RESULTS

The search identified 97 HIV-infected patients concomitantly receiving antiretroviral and antiepileptic drugs, for a total of 310 drug measurements. Overall, 30%, 64% and 6%, versus 28%, 65% and 7%, of the antiepileptic concentrations measured in HIV-infected versus HIV-negative patients (1090 patients, for a total of 3488 antiepileptic concentrations measured) were below, within, or above the therapeutic targets, respectively. The antiepileptic drug valproate was associated with the highest risk of subtherapeutic drug concentrations, with 57% and 46% of determinations below the therapeutic range in HIV-positive and HIV-negative patients, respectively. Remarkably, the concentrations of valproate were significantly lower in HIV-infected versus HIV-negative patients (47.9 ± 21.2 versus 53.9 ± 21.6 mg/L; p < 0.05).

CONCLUSION

In our retrospective study, most HIV-infected patients had antiepileptic drug concentrations falling within the therapeutic targets, with the exception of valproate, which was associated with a higher rate of subtherapeutic concentrations compared with other antiepileptic drugs.

Seizures in Children with HIV infection in South Africa: A retrospective case control study

PURPOSE

Data relating to the role that Human immunodeficiency virus (HIV) contributes towards seizures in HIV-infected children is limited. The management of seizures in this group is complex due to potential interactions between antiseizure medication and antiretroviral therapies. This study explores the seizure semiology and course of a population of affected children based on questions raised from a previous epidemiological study.

METHODS

A retrospective case-control study of all patients presenting to an HIV neurology clinic between 2008-2015 was conducted. A multinomial logistic regression model was used to identify risk factors for seizure occurrence in HIV-infected children, as well as factors associated with seizure control.

RESULTS

Of 227 HIV-infected children (median 82 months, interquartile range 41-109), 52 (23%) reported a past or present history of seizures. Prior bacterial meningitis (p =  0.03, OR 12.5, 95% CI 1.2-136.1), cerebrovascular accident (CVA, p =  0. 005, OR 8.1, 95% CI 1.9-34.9) and or tuberculous meningitis (TBM, p =  0.0004) was associated with an increased risk of seizures in HIV-infected children. Generalised tonic-clonic seizures were the predominant seizure type (64%) with the majority caused by an infectious aetiology (62%). Thirty-two (62%) of these patients had epilepsy in-line with the latest diagnostic criteria. HIV-infected children with epilepsy who were treated with efavirenz were more likely to have poor seizure control (OR 23.1 95% CI 3.4-159.6, p =  0.0001).

CONCLUSIONS

This study provides new data highlighting the complex clinical presentation and management challenges of HIV-infected children with seizures.

Drug-Drug Interactions and HIV Therapy: What Should Pharmacists Know?

Drug-interaction issues continue to present a major dilemma for the clinician caring for complex patients such as those infected with HIV. The inherent possibility of a drug interaction is magnified by the multitude of drugs being administered in highly-active antiretroviral therapy (HAART). In addition, other classes of medications are used to alleviate side effects, reduce toxicities associated with HAART, or treat concomitant diseases. The modification of one drug by another substance or drug-drug interaction is the main focus of this article. Drug-drug interactions may result in toxicity, treatment failure, or loss of effectiveness and can significantly affect a patient’s clinical outcome. An understanding of the fundamental mechanisms of HIV drug-drug interactions may allow for the early detection or avoidance of troublesome regimens and prudent management if they develop. Although HIV drug interactions are usually thought of as detrimental, resulting in a loss of therapeutic effect or toxicity, some drug interactions such as ritonavir boosted protease inhibitor–based antiretroviral treatments are beneficial and are commonly used in clinical practice. Therefore, pharmacists need to understand drug interaction mechanisms, remember key drug interactions, and vigilantly monitor patients for potential complications.

Safe Treatment of Seizures in the Setting of HIV/AIDS

OPINION STATEMENT

HIV(+) patients are at increased risk for developing seizures due to the vulnerability of the central nervous system to HIV-associated diseases, immune dysfunction, and metabolic disturbances. In patients with acute seizures, standard protocols still apply with urgent seizure cessation being the priority. Management of the person with established epilepsy who contracts HIV is challenging, but the decision to initiate chronic antiepileptic drug (AED) therapy in an HIV(+) patient is also difficult. Chronic treatment guidelines emphasize the interactions between AEDs and antiretroviral (ARV) medications, but provide no explicit advice regarding when to initiate an AED, what medication to select, and/or the duration of treatment. Epidemiologic data regarding seizure recurrence risk in HIV(+) individuals is not available. The risk of further seizures likely depends upon the underlying etiology for the seizure(s) and patients' immune status and may be increased by the use of efavirenz (an ARV). The issues for consideration include AED-ARV interactions, organ dysfunction, seizure type, and drug side effects, which may worsen or be confused with symptoms of HIV and/or epilepsy. Co-administration of enzyme inducing (EI)-AEDs and ARVs can result in virological failure, breakthrough seizure activity, AED toxicity, and/or ARV toxicity. Where available, the AED of choice in HIV(+) patients is levetiracetam due to its broad spectrum activity, ease of use, minimal drug interactions, and favorable side effect profile. Lacosamide, gabapentin, and pregabalin are also favored choices in patients with partial onset seizures and/or those failing levetiracetam. Where newer AEDs are not available, valproic acid may be the treatment of choice in terms of an AED, which will not cause enzyme induction-associated ARV failure, but its side effect profile causes other obvious problems. In resource-limited settings (RLS) where only EI-AEDs are available, there are no good treatment options and further pressure needs to be placed upon policymakers to address this care gap and public health threat.

Prevalence of seizures in children infected with human immunodeficiency virus

A retrospective study of 354 human immunodeficiency virus (HIV)-infected patients identified a subgroup of 27 children with seizures (7.6%, 95% confidence interval: 5.1%-10.9%). Of the total group, 13% (n = 46) had identifiable neurologic deficits and 30% (n = 107) had developmental delay. Both observations were significantly more frequent in the subgroup of patients with seizures (P < .001). The median age of patients with seizures was 20 months (range, 8-87 months) and the median baseline CD4 percentage was 13.5% (interquartile range, 8%-23%). Seizures were treated with sodium valproate (n = 11), phenobarbital (n = 3), diazepam (n = 2), lamotrigine (n = 1), and carbamazepine (n = 1). Combination therapy was required for 5 children. Suboptimal valproic acid levels were recorded for 3 patients. When resources are available, antiepileptic drug level monitoring is advised for children who require both antiepileptic and antiretroviral medications to facilitate optimal seizure management.

The impact of enzyme-inducing antiepileptic drugs on antiretroviral drug levels: a case-control study

PURPOSE

To evaluate the impact of enzyme-inducing antiepileptic drugs (EI-AEDs) on serum antiretroviral (ARV) levels in patients with HIV.

METHODS

Data from the U.S. Military HIV Natural History Study were screened to identify participants taking ARVs with EI-AEDs and controls taking ARVs with non enzyme-inducing AEDs (NEI-AEDs). The proportion of serum ARV levels below the recommended minimum concentrations (C(min)) was compared between these groups.

RESULTS

ARV levels were available for 10 individuals exposed to 16 intervals on combined ARVs/EI-AEDs (phenytoin and carbamazepine) and for 25 controls exposed to 30 overlap intervals on combined ARVs/NEI-AEDs. The percentage of overlap intervals with ≥1 ARV levels below C(min) was higher in the EI-AED group than in controls (37.5% vs. 23.3%; p=0.124). After excluding intervals associated with serum levels of EI-AEDs below the reference range (n=6), the proportion of intervals with ≥1 ARV level below C(min) was significantly greater among EI-AED recipients (60%) compared to controls (23.3%; p=0.008).

CONCLUSIONS

ARV levels below C(min) were more common in participants receiving EI-AEDs, the difference being statistically significant for intervals associated with EI-AED levels within the reference range. These data suggest that, in agreement with current guidelines, EI-AEDs should be avoided in patients receiving ARV therapy.

Neurologic and neurobehavioral sequelae in children with human immunodeficiency virus (HIV-1) infection

The range and extent of neurologic and neurobehavioral complications of human immunodeficiency virus (HIV-1) infection in children are under-described. Seventy-eight children with HIV-1 infection (32 females) were assessed for neurologic complications. Forty-six children had abnormal neurology examinations. Thirty-three children had global pyramidal tract signs, 5 had a hemiparesis, 4 had peripheral neuropathy, 18 had visual impairment, and 5 had hearing impairment. Thirty-nine of 63 children over 1 year of age had neurobehavioral problems. Of 24 children with HIV encephalopathy, 74% had severe immunosuppression and 45% were not receiving antiretroviral therapy. Twelve children had prior opportunistic central nervous system infections, and 9 had epilepsy. Diverse neurologic and neurobehavioral deficits are common in children with HIV-1 infection. Children with severe immunosuppression, who were not receiving antiretroviral therapy, were growth impaired and less than 1 year of age, were at greatest risk for developing neurologic complications.

Virologic outcomes of HAART with concurrent use of cytochrome P450 enzyme-inducing antiepileptics: a retrospective case control study

BACKGROUND

To evaluate the efficacy of highly-active antiretroviral therapy (HAART) in individuals taking cytochrome P450 enzyme-inducing antiepileptics (EI-EADs), we evaluated the virologic response to HAART with or without concurrent antiepileptic use.

METHODS

Participants in the US Military HIV Natural History Study were included if taking HAART for ≥6 months with concurrent use of EI-AEDs phenytoin, carbamazepine, or phenobarbital for ≥28 days. Virologic outcomes were compared to HAART-treated participants taking AEDs that are not CYP450 enzyme-inducing (NEI-AED group) as well as to a matched group of individuals not taking AEDs (non-AED group). For participants with multiple HAART regimens with AED overlap, the first 3 overlaps were studied.

RESULTS

EI-AED participants (n = 19) had greater virologic failure (62.5%) compared to NEI-AED participants (n = 85; 26.7%) for the first HAART/AED overlap period (OR 4.58 [1.47-14.25]; P = 0.009). Analysis of multiple overlap periods yielded consistent results (OR 4.29 [1.51-12.21]; P = 0.006). Virologic failure was also greater in the EI-AED versus NEI-AED group with multiple HAART/AED overlaps when adjusted for both year of and viral load at HAART initiation (OR 4.19 [1.54-11.44]; P = 0.005). Compared to the non-AED group (n = 190), EI-AED participants had greater virologic failure (62.5% vs. 42.5%; P = 0.134), however this result was only significant when adjusted for viral load at HAART initiation (OR 4.30 [1.02-18.07]; P = 0.046).

CONCLUSIONS

Consistent with data from pharmacokinetic studies demonstrating that EI-AED use may result in subtherapeutic levels of HAART, EI-AED use is associated with greater risk of virologic failure compared to NEI-AEDs when co-administered with HAART. Concurrent use of EI-AEDs and HAART should be avoided when possible.

Clinical outcomes and immune benefits of anti-epileptic drug therapy in HIV/AIDS

Background

Anti-epileptic drugs (AEDs) are frequently prescribed to persons with HIV/AIDS receiving combination antiretroviral therapy (cART) although the extent of AED use and their interactions with cART are uncertain. Herein, AED usage, associated toxicities and immune consequences were investigated.

Methods

HIV replication was analysed in proliferating human T cells during AED exposure. Patients receiving AEDs in a geographically-based HIV care program were assessed using clinical and laboratory variables in addition to assessing AED indication, type, and cumulative exposures.

Results

Valproate suppressed proliferation in vitro of both HIV-infected and uninfected T cells (p <0.05) but AED exposures did not affect HIV production in vitro. Among 1345 HIV/AIDS persons in active care between 2001 and 2007, 169 individuals were exposed to AEDs for the following indications: peripheral neuropathy/neuropathic pain (60%), seizure/epilepsy (24%), mood disorder (13%) and movement disorder (2%). The most frequently prescribed AEDs were calcium channel blockers (gabapentin/pregabalin), followed by sodium channel blockers (phenytoin, carbamazepine, lamotrigine) and valproate. In a nested cohort of 55 AED-treated patients receiving cART and aviremic, chronic exposure to sodium and calcium channel blocking AEDs was associated with increased CD4+ T cell levels (p <0.05) with no change in CD8+ T cell levels over 12 months from the beginning of AED therapy.

Conclusions

AEDs were prescribed for multiple indications without major adverse effects in this population but immune status in patients receiving sodium or calcium channel blocking drugs was improved.

Seizure management in a complex hospice patient

Antiepileptic medication use in noncancer hospice/palliative care patients is not well defined. The authors report the case of a human immunodeficiency virus (HIV) patient under hospice care with increased seizure frequency. The patient is a 22-year-old female with advanced HIV disease complicated by tonic-clonic seizures, hypoalbuminemia, gastroesophageal reflux disease (GERD), and gastritis. During an admission to the hospice inpatient unit, she developed increasing seizure frequency while receiving oral phenytoin. After collaboration between the clinical pharmacist and the hospice treating physician, they simplified her medication regimen, discontinued the phenytoin, and initiated oral levetiracetam. After these adjustments to her medication regimen, the patient's seizure frequency decreased significantly. This case illustrates the challenges of anticonvulsant use in advanced disease, including drug-drug interactions, impaired pharmacokinetics parameters, and increased risk of adverse effects. The importance of continuously monitoring patients for adverse drug events and assessing patient specific factors to help guide medication selection are also highlighted.

Potential drug-drug interactions with antiepileptic drugs in Medicaid recipients

PURPOSE

The frequency of potential drug-drug interactions (DDIs) between antiepileptic drugs (AEDs) and other (non-AED) medications in Medicaid patients taking newer AED monotherapy, older AED monotherapy, and combinations of AED treatment was studied.

METHODS

A retrospective, observational study was conducted using administrative claims obtained from South Carolina Medicaid. Patients were included in the analysis if they (1) had at least one prescription for an AED between January 1, 2004, and December 31, 2004, (2) were taking a specific AED for at least 60 days, (3) had at least one epilepsy diagnosis during the 6 months before or during the enrollment period, and (4) were enrolled in Medicaid for at least 11 of the 12 months of the follow-up period. Possible DDI exposure was defined as 10 days of overlap between an AED and a non-AED known to have the potential to cause a clinically relevant interaction.

RESULTS

A total of 4955 patients met the inclusion criteria. Approximately 45% of patients receiving monotherapy with an older AED had a potential DDI, compared with 3.9% receiving a newer AED. An average of 0.08 potential DDI per year of exposure occurred in the newer AED monotherapy cohort compared with 1.18 in the older AED monotherapy cohort. The most common potential interaction category was a decreased concentration of the non-AED.

CONCLUSION

Older AEDs were associated with a greater likelihood of a potential DDI than were newer AEDs. Further research is needed to elucidate the relationship between the occurrence of potential DDIs and actual clinically relevant consequences.

Possible antiretroviral therapy-warfarin drug interaction

Highly active antiretroviral therapy (HAART) for human immunodeficiency virus (HIV) has resulted in significant morbidity and mortality reductions. Lifelong antiretroviral therapy must be incorporated into each patient's medical regimen. Patients with HIV may also have simultaneous chronic medical conditions, resulting in the possibility of complex drug-drug interactions. We report a possible drug-drug interaction between HAART and warfarin in two patients, as assessed by the Naranjo adverse drug reaction probability scale and the Drug Interaction probability scale. Both patients' pharmacotherapy regimens included a nonnucleoside reverse transcriptase inhibitor (NNRTI), nevirapine, or a protease inhibitor, nelfinavir or lopinavir-ritonavir, and two nucleoside analogs. In both patients, high warfarin doses were required to maintain therapeutic international normalized ratios (INRs). Warfarin has two enantiomers, R-and S-warfarin, which are substrates primarily of cytochrome P450 (CYP) 3A4 (R-warfarin), CYP1A2 (R-warfarin), and CYP2C9 (S-warfarin). Protease inhibitors and NNRTIs have variable effects on CYP: induction, inhibition, or mixed. The increased warfarin doses required in these two patients may have been caused by induction of CYP3A4 by nevirapine, CYP2C9 by nelfinavir, or CYP2C9 by lopinavir-ritonavir. Thus, practitioners should prudently monitor INRs in patients receiving warfarin with concomitant HAART that includes either a protease inhibitor or an NNRTI.

Frequency of seizures and epilepsy in neurological HIV-infected patients

BACKGROUND

Infection with the human immunodeficiency virus (HIV) is associated both with infections of the central nervous system and with neurological deficits due to direct effects of the neurotropic virus. Seizures and epilepsy are not rare among HIV-infected patients. We investigated the frequency of acute seizures and epilepsy of patients in different stages of HIV infection. In addition, we compared the characteristics of patients who experienced provoked seizures only with those of patients who developed epilepsy.

METHODS

The database of the Department of Neurology, University of Münster, was searched for patients with HIV infection admitted between 1992 and 2004. Their charts were reviewed regarding all available sociodemographic, clinical, neurophysiological, imaging and laboratory data, therapy and outcome. Stage of infection according to the CDC classification and the epileptogenic zone were determined.

RESULTS

Of 831 HIV-infected patients treated in our department, 51 (6.1%) had seizures or epilepsy. Three of the 51 patients (6%) were diagnosed with epilepsy before the onset of the HIV infection. Fourteen patients (27%) only had single or few provoked seizures in the setting of acute cerebral disorders (eight patients), drug withdrawal or sleep withdrawal (two patients), or of unknown cause (four patients). Thirty-four patients (67%) developed epilepsy in the course of their HIV infection. Toxoplasmosis (seven patients), progressive multifocal leukencephalopathy (seven patients) and other acute or subacute cerebral infections (five patients) were the most frequent causes of seizures. EEG data of 38 patients were available. EEG showed generalized and diffuse slowing only in 9 patients, regional slowing in 14 patients and regional slowing and epileptiform discharges in 1 patient. Only 14 of the patients had normal EEG. At the last contact, the majority of the patients (46 patients=90%) were on highly active antiretroviral therapy (HAART). Twenty-seven patients (53%) were on anticonvulsant therapy (gabapentin: 14 patients, carbamazepine: 9 patients, valproate: 2 patients, phenytoin: 1 patient, lamotrigine: 1 patient). Patients with only provoked seizures had no epilepsy risk factors except HIV infection, and were less likely to be infected via intravenous drug abuse.

CONCLUSIONS

Seizures are a relevant neurological symptom during the course of HIV infection. Although in some patients seizures only occur provoked by acute disease processes, the majority of patients with new onset seizures eventually develops epilepsy and require anticonvulsant therapy. Intravenous drug abuse and the presence of non-HIV-associated risk factors for epilepsy seem to be associated with the development of chronic seizures in this patient group.

Clinically relevant drug interactions with antiepileptic drugs

Some patients with difficult-to-treat epilepsy benefit from combination therapy with two or more antiepileptic drugs (AEDs). Additionally, virtually all epilepsy patients will receive, at some time in their lives, other medications for the management of associated conditions. In these situations, clinically important drug interactions may occur. Carbamazepine, phenytoin, phenobarbital and primidone induce many cytochrome P450 (CYP) and glucuronyl transferase (GT) enzymes, and can reduce drastically the serum concentration of associated drugs which are substrates of the same enzymes. Examples of agents whose serum levels are decreased markedly by enzyme-inducing AEDs, include lamotrigine, tiagabine, several steroidal drugs, cyclosporin A, oral anticoagulants and many cardiovascular, antineoplastic and psychotropic drugs. Valproic acid is not enzyme inducer, but it may cause clinically relevant drug interactions by inhibiting the metabolism of selected substrates, most notably phenobarbital and lamotrigine. Compared with older generation agents, most of the recently developed AEDs are less likely to induce or inhibit the activity of CYP or GT enzymes. However, they may be a target for metabolically mediated drug interactions, and oxcarbazepine, lamotrigine, felbamate and, at high dosages, topiramate may stimulate the metabolism of oral contraceptive steroids. Levetiracetam, gabapentin and pregabalin have not been reported to cause or be a target for clinically relevant pharmacokinetic drug interactions. Pharmacodynamic interactions involving AEDs have not been well characterized, but their understanding is important for a more rational approach to combination therapy. In particular, neurotoxic effects appear to be more likely with coprescription of AEDs sharing the same primary mechanism of action.

Pharmacokinetic drug interactions with non-nucleoside reverse transcriptase inhibitors

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are a diverse group of compounds that inhibit HIV Type 1 reverse transcriptase. Although possessing a common mechanism of action, the approved NNRTIs, delavirdine, efavirenz and nevirapine, differ in structural and pharmacokinetic characteristics. Each of the NNRTIs undergoes biotransformation by the cytochrome P450 (CYP) enzyme system, thus making them prone to clinically significant drug interactions when combined with other antiretrovirals. In addition, they interact with other concurrent medications and complementary/alternative medicines, acting as either inducers or inhibitors of drug-metabolising CYP enzymes. These drug interactions become an important consideration in the clinical use of these agents when designing combination regimens, as recommended by current guidelines. This review provides an updated summary of pharmacokinetic interactions with NNRTIs.

Increased adverse drug reactions to antimicrobials and anticonvulsants in patients with HIV infection

OBJECTIVE

To review the incidence, signs, symptoms, and mechanisms of adverse drug reactions (ADRs) to sulfonamides, anticonvulsants, and antimycobacterial medications among people with HIV.

DATA SOURCES

Searches of MEDLINE/PubMed (1980-November 2005) and National Library of Medicine Meeting Abstracts (1989-November 2005), as well as hand searches of journals and abstracts, were conducted to identify primary literature. Reference lists were reviewed to identify additional relevant reports.

STUDY SELECTION AND DATA EXTRACTION

Relevant articles and abstracts, particularly of in vitro experiments and clinical studies, were compiled and reviewed.

DATA SYNTHESIS

ADRs, especially in HIV-infected patients, are a cause for concern. Sulfonamides, anticonvulsants, and antimycobacterial drugs are commonly used to prevent and treat complications of HIV, including seizures and opportunistic infections. Patients with HIV have a much greater rate of ADRs to these drug classes, including severe and life-threatening hypersensitivity reactions. Several mechanisms of these ADRs have been postulated. Sulfamethoxazole and anticonvulsant hypersensitivity may involve the increased formation and decreased detoxification of reactive metabolites. The mechanisms for the marked increase in hypersensitivity ADRs to antimycobacterial drugs may be related to an altered immune profile in patients infected with both tuberculosis and HIV.

CONCLUSIONS

ADRs to antimicrobial and anticonvulsant therapy cause markedly increased morbidity and mortality in HIV-positive patients. Further research involving the interaction between HIV and the increased ADRs to these drugs is required.

Carbamazepine toxicity induced by lopinavir/ritonavir and nelfinavir

OBJECTIVE

To present a case of carbamazepine toxicity induced by lopinavir/ritonavir and nelfinavir.

CASE SUMMARY

A 50-year-old HIV-positive male developed excessive drowsiness secondary to carbamazepine when an antiretroviral regimen containing lopinavir/ritonavir was introduced. The carbamazepine serum concentration increased 46%. Subsequently, the patient developed a possible adverse skin reaction to his antiretrovirals and was hospitalized. The protease inhibitor was changed to nelfinavir. Within 3 days, the patient again developed excessive drowsiness and became unsteady on his feet. This time, the carbamazepine serum concentration had increased by 53%. In both instances, the carbamazepine dosage was decreased by 33%, which resulted in resolution of symptoms.

DISCUSSION

Carbamazepine undergoes extensive hepatic metabolism. The major metabolic pathway involves oxidation of carbamazepine via CYP3A4 to an active metabolite, carbamazepine-10,11-epoxide. Protease inhibitors are well-known CYP3A4 inhibitors. Other cases of carbamazepine toxicity secondary to protease inhibitors are reviewed. A MEDLINE search (1966-May 2006) revealed 4 cases of carbamazepine toxicity secondary to antiretrovirals. Carbamazepine serum concentrations increased two- to threefold from baseline. Vertigo, drowsiness, disorientation, ataxia, and vomiting occurred within 12 hours to 2 months, which resolved with reduction of the carbamazepine dosage.

CONCLUSIONS

An objective causality assessment suggests that our patient became drowsy and unsteady on his feet secondary to a carbamazepine-protease inhibitor interaction. Lopinavir/ritonavir and nelfinavir may decrease carbamazepine metabolism, causing an elevation in carbamazepine serum concentrations. Carbamazepine toxicity may be prevented by reducing the carbamazepine dosage by 25-50% when protease inhibitors are introduced. A carbamazepine serum concentration should be repeated 3-5 days after the protease inhibitors are started.

Psychotropic medications and HIV

Patients with human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome have high rates of psychiatric illness. The effective management of these psychiatric conditions can improve a patient's quality of life and may improve antiretroviral adherence. Care providers for patients with HIV infection frequently encounter clinical situations in which psychotropic medications are needed or are being used. Those clinical situations require familiarity with the broad category of medications termed "psychotropic." That familiarity should include a basic understanding of indications, adverse effects, and drug interactions. In particular, it is very important to recognize the many potential interactions based on cytochrome P450 metabolism, which is common to many psychotropics, the protease inhibitors, and the nonnucleoside reverse-transcriptase inhibitors. In a brief review of the use of psychotropic medications in patients with HIV infection, we discuss indications, adverse effects, and drug interactions for commonly used antidepressants, mood stabilizers, anxiolytics, antipsychotics, psychostimulants, and drugs of abuse.

Highly active antiretroviral therapy and the kidney: an update on antiretroviral medications for nephrologists

Highly active antiretroviral therapy has dramatically altered the treatment and life expectancy of individuals who are infected with HIV. More than 20 antiretroviral drugs and drug combinations now are available in the United States. Nephrologists need to have an understanding of the pharmacokinetics of antiretroviral medications and the proper dosing of these medications in patients with impaired kidney function. It is also important for nephrologists to be aware of drug-drug interactions that can occur between antiretroviral medications and other medications that they may prescribe, including immunosuppressive medications that are used for renal transplantation, as this becomes more common in HIV-infected patients. Adverse reactions that affect the kidneys and cause fluid-electrolyte complications occur with certain antiretroviral agents, although most are relatively free of nephrotoxicity. This article reviews the clinical pharmacology and dosing modifications of the newer antiretroviral medications in patients with reduced kidney function; important drug-drug interactions involving these medications, particularly with other medications that are likely to be prescribed by nephrologists; and renal toxicities of antiretroviral agents.

Altered Cytochrome P450 Metabolism of Calcineurin Inhibitors: Case Report and Review of the Literature

A 19-year-old woman was admitted to receive a kidney transplant from a nonliving donor. At the time of transplantation, she was taking oral phenytoin 300 mg every morning, 100 mg at noon, and 300 mg every evening (total of 700 mg/day) to treat seizures secondary to hemodialysis. Immediately after the transplantation, phenytoin treatment was resumed, and immunosuppressive therapy consisting of antithymocyte globulin, cyclosporine, mycophenolate mofetil, and corticosteroids was started. Her cyclosporine blood levels varied over the first 10 days after transplantation. Cyclosporine was discontinued, and tacrolimus was begun after acute rejection was discovered. The rejection was treated with antithymocyte globulin, plasmapheresis, and intravenous immunoglobulin, and subsequently resolved; however, the patient's blood concentrations of tacrolimus varied widely. Phenytoin is an antiepileptic drug that induces hepatic enzymes, affecting the cytochrome P450 3A family. These enzymes metabolize approximately 50% of all prescribed drugs, including cyclosporine and tacrolimus. According to the Naranjo adverse drug reaction probability scale, this patient's adverse drug reaction probably occurred from altered metabolism of cyclosporine and tacrolimus due to phenytoin therapy. Clinicians must identify drug interactions between metabolic enzyme inducers or inhibitors and drug substrates with narrow therapeutic ranges, closely monitor drug concentrations, and observe patients for clinical signs and symptoms of therapeutic failure or toxicity. In daily practice, clinicians should explore the metabolic characteristics of drugs and their biotransformation pathways to identify patients who require alternative therapy.

Drug interactions in the management of HIV infection

The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.